Cigarette smoking is the leading cause of preventable death and illness in the United States and throughout the developed world. Currently, the tobacco industry focuses over 80% of its marketing budget in the retail environment. Recent work suggests detrimental links between exposure to point-of-sale tobacco marketing (POSTM), increases in cigarette cravings, and the failure to quit smoking. Understanding how individuals are influenced by and react to their natural environments when making health decisions is thus critical to cancer control efforts. We propose to use an innovative set of methods to test whether repeated, real-world exposure to POSTM affects smoking behavior, and whether this is mediated by heightened craving and neural responses to POSTM. Our novel multi-method approach to communication research includes mobile-phone based geolocation tracking, ecological momentary assessment (EMA), and functional magnetic resonance imaging (fMRI). By adding the ecological validity of observational field methods to the mechanistic insight of neuroimaging, and causal inferences from an experimental design, we aim to significantly advance actionable insight about POSTM effects in cancer control. Research utilizing geospatial location tracking and survey methods suggests that high levels of POSTM exposure may increase craving; however, correlational studies preclude mechanistic explanations and causal inferences about POSTM effects. Relatedly, laboratory studies have documented neural and behavioral reactivity to standardized visual smoking cues, such as photographs of cigarettes, but the brain?s response to naturalistic POSTM exposure has not been explored. We hypothesize that exposure to POSTM increases brain responses to smoking cues as well as subjective craving, leading to increased smoking behavior. To test this, we will follow 180 daily smokers with geospatial location tracking and EMA to assess whether longitudinal fluctuations in real-world POSTM exposure are associated with moment-to-moment cigarette craving and smoking behavior (Aim 1), and whether these processes are related to differences in neural smoking cue reactivity (Aim 2). Finally, we will conduct an experiment that manipulates naturalistic exposure to POSTM to test whether these effects are causal (Aim 3). In the experimental phase, two groups of participants will enter and make a small purchase (e.g., water) at a retail outlet with or without POSTM displays 5 times per week for 4 weeks, while a third control group will not change their habits. We will measure neural responses and subjective cravings to POSTM exposure in all groups before and after the experimental manipulation. Protocol feasibility and dosage has been established through extensive pilot work. Increases in smoking behavior, craving, and/or neural cue reactivity in response to increased POSTM exposure would strongly implicate causal evidence for POSTM exposure, which is much needed for science-based policy making and could inform cancer control efforts.causal evidence for POSTM exposure, which is much needed for science-based policy making and could inform cancer control efforts.